1. Field of the Invention
The present invention relates to wipe solvent-primer compositions for application to various substrates, including bare metal, metal having a surface finish/coating such as anodized, Alodined, deoxidized, or abraded metals, fiberglass, plastic films, organic coatings, composites, glass and other substrates, for purposes of cleaning and priming the substrate surface to improve the receptivity and bonding properties of the substrate relative to organic coatings, adhesives, adhesive coatings, sealants, paints, honeycomb structures and similar materials conventionally bonded to such substrates.
2. State of the Art
It is known to improve the receptivity of substrates for paints, primers and adhesive layers by treating the substrate surface with mechanical abrasive operations such as blasting followed by cleaning with an organic solvent such as methyl ethyl ketone followed by brush-coating with a dilute aqueous silane solution and drying. Reference is made to U.S. Pat. No. 5,312,520 to Chung, dated May 17, 1994, and entitled “Method of metallic surface preparation utilizing silane for adhesive bonding” The process according to this patent is objectionable because methyl ethyl ketone is a hazardous air pollutant, dangerous to worker safety, and the process requires three separate steps, with the silane brushing step being repeated three times using alternating brush strokes.
Reference is made U.S. Pat. No. 5,424,133 to Eckhardt, et al., dated Jun. 13, 1995, and entitled “Process for the preparation of substrate surfaces for adhesive bonding” for its disclosure of a process for preparing a plastic film or composite substrate surface for adhesive bonding coating operations by applying to the surface an abrasive composition containing abrasive particles such as silicon-containing particles and rubbing the coating into the surface to fix the abrasive particles thereto. The surface is first degreased by wiping with a solvent such as isopropanol.
It is known to treat or coat aluminum and other substrates to improve their bonding properties relative to primers, paints, adhesive coatings and other substrates such as composites, metals, glass, etc. Such process typically requires the use of a chemical conversion coating (CCC), such as Alodine, over the aluminum surface to improve the bonding properties of the substrate for paints, adhesives, etc., while enhancing the corrosion resistance of the coating system. The chemical conversion coating composition typically contains chromic acid, a fluoride acid salt and accelerators.
Chromium is an environmentally-objectionable chemical targeted by the EPA for reduction or elimination, and the replacement of chromium-containing plating and treatment baths with non-chromated baths has been the subject of extensive academic and industrial research.
Alternative chromium-free coating compositions have been developed but the process of applying such compositions requires multiple steps, each of which usually requires a different heated process tank as opposed to the single heated process tank required for the conventional chromated chemical conversion coating (CCC) process. The energy and facility requirements of this alternative process create substantial difficulty and expense from the standpoint of implementation into a production facility.
Another alternate chemical conversion process involves the use of a cobalt-amine oxidizing composition such as Alodine 2000 to form a chemical oxide film on aluminum substrates. Such process requires the use of two separate heated process tanks. In the first step a chemical oxide layer is formed on the surface of the aluminum using a cobalt-amine oxidizing bath to form an oxide layer about 1000 angstrom units in thickness. In the second step the oxidized aluminum substrate is immersed in a second tank containing a composition which seals the oxide layer to impart corrosion resistance to the substrate. The first step increases the bonding properties of the aluminum substrate while the second step is required to impart corrosion resistance.
Presently, when a silicone composition is applied to various substrates, it is often necessary to use a primer; that is, a primer is applied on the surface of the substrate and then the silicone composition is applied thereover and cured onto the substrate. In many cases, if a silicone composition is applied to a substrate without a primer, the bond between the silicone and the substrate is not as strong as would be desired.
Application of a primer entails an additional step in the preparation of the substrate and thus is costly as well as time consuming. Therefore, it would be desirable to provide silicone compositions which do not require a primer to be applied to the surface of the substrate.
The use of silylfumarate and silylmaleate compounds as adhesion promoters in silicone compositions is known in the art. De Zuba et al., U.S. Pat. No. 3,941,741 discloses the use of a maleate, fumarate, silylmaleate, or silylfumarate compound as a self-bonding additive in a heat-curable silicone rubber composition. U.S. Pat. No. 4,273,698 to Smith, Jr., et al., dated Jun. 16, 1981 and entitled “Self-bonding room temperature vulcanizable silicone rubber compositions”; U.S. Pat. No. 4,308,372 to Smith, Jr., et al., dated Dec. 29, 1981 and entitled “Shelf-stable one-part room temperature vulcanizable silicone rubber composition” and U.S. Pat. No. 4,395,507 to Dziark, et al., dated Jul. 26, 1983 and entitled “Self-bonding one-component dimedone RTV silicone rubber compositions” disclose the use of a silyl maleate, a silyl fumarate, or a silyl succinate as an adhesion promoter in room temperature curable silicone compositions.
The use of silylfumarate and silylmaleate compounds as adhesion promoters in addition-curable silicone compositions is also known in the art. [U.S. Pat. No. 4,891,407 to Mitchell, dated Jan. 2, 1990 and entitled “Interpenetrating polymeric networks comprising polytetrafluoroethylene and polysiloxane”: U.S. Pat. No. 5,164,461, to Mitchell, et al., dated Nov. 17, 1992 and entitled “Addition-curable silicone adhesive compositions”).
Alkanolamines incorporated with aminosilanes into surface films have been discovered to provide exceptional levels of adhesive performance when overcoated with any of a variety of paints and polymers. [U.S. Pat. No. 6,020,028 to Kinneberg, dated Feb. 1, 2000 and entitled “Silane adhesion catalysts”] That method involves applying a solution of an aminosilane and an alkanolamine, dissolved in a solvent, to a substrate and thereafter contacting the coated substrate surface with uncured paint or fluid polymer and allowing the uncured paint or fluid polymer to cure.
U.S. Pat. No. 6,096,700 to Weir, et al. dated Aug. 1, 2000 and entitled “Environmental wipe solvent compositions and processes”, discloses a wipe solvent use containing compositions of an environmentally safe volatile organic solvent and a minor volume of a poly-functional coupling agent, preferably of the silane type.
Recently work has been done [U.S. Pat. No. 6,004,679 to Mitchell, et al. dated Dec. 21, 1999 and entitled “Laminates containing addition-curable silicone adhesive compositions”] on a process to add an adhesion promoter directly to silicone coating materials for added adhesion to substrates. Clearly, it is highly desirable to provide a process, which eliminates the need for chemical conversion steps which require the use of chromium or require the use of several heated baths and several steps to enhance adhesion properties to the substrate.
Such processes are tedious, time-consuming, cost-ineffective and/or dangerous, and are unsatisfactory for use on certain substrates, where abrasion or blasting cannot be used, and are ineffective for certain coatings and bonding operations.
Therefore, it is an object of this invention to provide a process for preparing a substrate with enhanced adhesion properties.
It is an object of this invention to provide a process for preparing a substrate with enhanced adhesion properties while eliminating a process step in preparing the substrate.
It is an object to provide a process for preparing a substrate with enhanced adhesion properties without requiring the use of noxious, hazardous or environmentally unfriendly substances.